GEOLOGICAL SUKVEY OF THE TEKRITOEIES. 247 



row fissure, along which for 6 or 8 feet the water boils constautly. Near 

 this is a small ge^'ser-uiound strongly colored with iron. 



On the opposite side of the creek is a broad terrace of the siliceous 

 spring-deposits, upon which stand several small mounds very prettily 

 ornamented, from 1 foot to 2 feet high, whose pools boil considerably, and 

 evidently spout occasionally, though no one of them was seen iu eruption. 

 One of these, near the creek and nearly opposite to Minute Man, is 

 shaped like a conch-shell and strongly colored with iron, and was called 

 Iron-Conch Geyser. 



Xearer the base of the hills, there are severnl large hot pools. One of 

 them was so well furnished with coralliform masses, standing in the 

 shallow water near its edge, as to be called the Coral Pool. This meas- 

 ured about 40 feet by 50, with a shallow border, and a deep central pit 

 about 10 feet across, from which numerous bubbles of gas were escap- 

 ing. There is a strong flow of water of the temperature of 160°. A 

 little to the west of this, a valley runs well uj) into the hills and contains 

 several large boiling i3oo]s, but no geysers. One boils with great vio- 

 lence, with a very large escape of steam. The pools and old deserted 

 basins extend up the slopes of the hills to elevations of from 100 to 150 

 feet above the creek. 



As a whole, these springs and geysers show far greater amounts of 

 sulphur, and especially of iron, in their deposits than any of those on the 

 Madison. The geysers also show much greater irregularities of erup- 

 tions. The group seems to me, as a whole, younger than those in the 

 Fire-Hole Basins. The little geysers on the west side of the creek are 

 plainly young, and are just beginning mounds which promise to attain 

 considerable size. 



On the east side of the creek, between it and the lakes, we find a clus- 

 ter of ragged hills, separated by crateriform hollows and valleys, which 

 are occupied more or less completely by mud-springs and sulphur-vents. 

 Upon breaking up the surface-crust about these latter, we find all its 

 hollows lined with sulphur, either in distinct crystals or in moss-like 

 aggregations of imperfect ones. Upon first observing the shape and 

 contents of these hollows, one would naturally suppose them to be old 

 volcanic craters, whose connections with the interior fires were becom- 

 ing nearly stopped up ; but, upon more careful examination, it becomes 

 evident that they have been hollowed out of the surrounding sandstone 

 by the action of the hot springs themselves, which have disintegrated 

 and removed portions of the sandstone and conglomerate of the old 

 lake-terrace. Worn bits of rocks, penetrated by numerous small irreg- 

 ular holes, are abundant on all the lower parts of the slopes, as well as 

 about the existing vents, showing that the process is still going on. 

 These springs are evidently much affected by variations in the supply 

 of water. Many which were entirely dry gave abundant evidence th j. t 

 they sometimes give forth considerable streams. The effects of these 

 variable supplies upon the activity of the different springs and geysers 

 are probably very different in different cases. Since a full basin seems 

 to be essential to an eruption, a greater supply of water to fill the place 

 of that ejected would, in many cases, cause more frequent and powerful 

 eruptions. On the other hand, it is probable that too large a supply, 

 causing a continuous stream to pass through and escape from the basin 

 of a geyser, would cool down its contents below the temperature essen- 

 tial to an eruption. 



The springs extend eastward along the shore of the lake for several 

 miles near its present level, and some were seen boiling up from its 

 bottom, several yards from shore. Many occur also in the marsh about 



